Bombardment-induced modification of GaAS/AlGaAs heterostructures

We have irradiated some GaAs/AlGaAs heterostructures with 80 keV He⁺ ions and studied bombardment-induced changes of the electrical resistivity and the carrier density of a two-dimensional electron layer located at the intersection between a GaAs buffer and an AlGaAs spacer. The whole structure was so thin that the projectiles passed through the two-dimensional electron layer and stopped in the supporting substrate. The resistivity and the carrier density of the samples were determined at temperatures between 1.2 and 4.2. K before and after the bombardments, which were carried out at room temperature. The carrier density was determined from Shubnikov-De Haas oscillations. An interesting result is that the resistivity depends strongly on the projectile fluence, in contrast to the carrier density. As an example, a fluence of 3 × 10⁹ He+ions/cm² doubles the resistance but reduces the carr density by 5% only.